This application claims the right of priority of German patent application No. 199 19 715.6, filed Apr. 30, 1999, and German patent application No. 100 14 560.4, filed Mar. 23, 2000, the disclosures of which are both incorporated herein by reference.
The invention relates to a coolant line for air-conditioning systems operated with carbon dioxide as a coolant, particularly air-conditioning systems of motor vehicles, in which the line is connected tightly, particularly by being welded, at both ends to connecting parts for connection with further components.
Air-conditioning systems for motor vehicles have been operated with chlorofluorocarbon-containing coolants. Because of the relatively low pressure, namely in the range of 30 to 40 bar, these coolants have presented no problems in the use of flexible, elastomer coolant lines, which have the capacity for relative movement between the line parts to be connected, and are desirable or necessary for damping vibrations.
Because of environmental concerns and because carbon dioxide is easier to dispose of, there is a growing demand for carbon dioxide as a coolant. Since, however, carbon dioxide must be used in the liquid state, it is under considerable pressure, specifically up to 200 bar, so the known flexible elastomer hoses, which are pervious to carbon dioxide, can no longer be used. Instead, pressure-stable and impervious, rigid, smooth lines must be used, which do not sufficiently absorb relative movements. Furthermore, the connecting parts welded to the ends of these lines encounter stability problems due to vibrations.
It is therefore an object of the invention to provide a flexible coolant line that can absorb the relative movements of adjacent parts to the necessary extent, and can particularly damp the vibrations caused by the coolant compressor without the danger of friction-induced wear.
In accordance with the invention, this object and others to become apparent as the application progresses, are accomplished by the invention, which pertains to a coolant line for use with air conditioning systems operating with carbon dioxide as a coolant that comprises ends to connect the coolant line to the air conditioning system an inner, metallic, coolant-tight corrugated hose having crests and two hose ends each connected to a connecting part. A flexible metal jacket has two jacket ends each connected to respective connecting parts. The jacket surrounds the corrugated hose to provide an axial support resisting radial pressure in the coolant line. The jacket is spaced from the corrugated hose crests by a radial spacing. A substantially incompressible, temperature resistant intermediate plastic layer fills at least the radial spacing between the flexible metal jacket and the crests to prevent play between the corrugated hose and the jacket.
With these features, a corrugated hose comprising a known, flexible material performs the function of gas-tight guidance of the coolant. Because a hose alone may not withstand the high pressures and pressure pulsations coming from the coolant compressor, it is provided with a radially pressure-resistant, flexible metal jacket that supports the axial forces developed by the corrugated hose as it seeks to expand under internal-pressure stresses. To avoid a frictional contact between the corrugated hose and the metal jacket that could result in the destruction of the crests of the corrugated hose due to vibrations and pressure pulsations, a substantially compression-proof, plastic intermediate layer is provided between the corrugated hose and the metal jacket. This intermediate layer is capable of transmitting the necessary radial support forces between the corrugated hose and the metal jacket, and simultaneously performs the function of damping vibrations, such as pulsations originating from the coolant compressor.
The invention provides a line element that is suited for high pressures, possesses the necessary degree of flexibility and, at the same time, damps vibrational stresses and pressure-pulsation stresses.
The corrugated hose could be a metal hose provided with a threaded corrugated texture. Because of the torsional movements caused between the ends of the metal hose due to high internal pressures, it is preferred for the corrugated hose to comprise a stainless-steel, corrugated hose such as an annularly corrugated hose.
The metal jacket can be a braided-cable hose or a hose knitted from stainless-steel wires. A braided-cable hose is preferred for its ability to absorb higher support forces. The stretching stress exerted externally by the corrugated hose presses the braided-cable hose tightly against the plastic intermediate layer, so the hose is then sufficiently capable of supporting radial stresses originating from the high internal pressure stress of the corrugated hose.
It is considered especially advantageous for the metal jacket to be a stripwound metal hose with an interlocked profile, preferably disposed in a stretched position when in the mounted position of the line. This type of stripwound metal hose with interlocked profile is substantially rigid with respect to radial stress, so it can support radial expansions of the corrugated hose very well, even from high internal-pressure stress. It can also support the corrugated hose against a change in length caused by internal-pressure stress if it is installed such that it is in a stretched position when in the final position of the coolant line. This final mounted position can be a straight line or a curve.
A stripwound metal hose with interlocked profile is also capable of damping vibrations to a certain extent because of the mutual friction of the strip edges, which are folded together during the production of the hose. It can be advantageous for the packing density or strength of the interwoven strip segments of the stripwound metal hose with interlocked profile to be matched to the vibration damping required for the line through more or less tight weaving of the strips during production, so the hose offers more or less resistance to the mutual axial displacement of adjacent strip windings.
The intermediate layer between the corrugated hose and the jacket surrounding it with radial spacing can comprise a plastic that is foamed onto the outside of the corrugated hose, completely filling the outer contour of the corrugated hose and offering a smooth, cylindrical surface for pairing with the jacket. An intermediate layer of this type is partially compressible due to the gas bubbles it contains, but this compressibility is limited to that required to provide the necessary flexibility of the corrugated hose and adequate support of radial force. If especially high requirements are to be placed on the incompressibility of the intermediate layer, the material of the layer can be selected to have no gas bubbles.
A different design can involve forming the intermediate layer from a plastic hose that is slid onto the corrugated hose. This type of plastic hose is incompressible, and can therefore perform the support function for the corrugated hose without limitations. It is advantageous if the inside of the plastic hose is provided with a profiling that is adapted to the peaks of the radially-outside corrugation crests, and is slid onto the corrugated hose with a prestressing that is directed radially inward, so that it is thereby secured against displacement on the corrugated hose. This arrangement also facilitates the subsequent mounting of the outside metal jacket.
As mentioned above, the intermediate layer has free ends. It is preferred that the intermediate layer fill all of the radially-outward-projecting corrugation crests of the corrugated hose, so the intermediate layer can absorb all friction between the corrugated hose and the jacket caused by vibrations and pressure pulsations, in addition to the radial support of the corrugated hose. The plastic of the intermediate layer can be a temperature-stabilized elastomer, such as, preferably, silicone gum or silicone rubber.
It is preferable for the intermediate layer to be tightly connected to the connecting parts, because in this way the intermediate layer not only prevents the outside corrugation crests of the corrugated hose from fraying, but also offers effective protection against the entry of external impediments and, therefore, corrosion of the hose.
Preferably, the connecting parts for the coolant line are metal tubular pieces having a collar that is mounted in the region of the line-side end and projects radially outward. The collar can be formed from the metal tubular piece by radial expansion or folding. In such an embodiment, the jacket can then be connected, for example by welding, to the circumferential surface of the collar. Particularly for a jacket formed from a metal-wire braid, it is also possible for the jacket to extend beyond the respective collar and rest against the outer collar circumference, while its ends are secured, preferably by being welded, to the associated metal tubular piece on the other side of the collar with respect to the corrugated hose. This embodiment supports the transition of the jacket from the metal tubular piece, which has a smaller diameter, to the outside diameter formed by the corrugated tube with the mounted intermediate layer, during expansion or folding, to provide support at the diameter transition without additional stress at the end-side corrugations of the corrugated hose. The jacket ends can also be surrounded by an inserted metal support ring welded, with the jacket ends, to the metal tubular pieces.
The ends of the corrugated hose can be connected, preferably by being welded, to the radially-inside base of the respective associated collar, in which case it is advantageous that the metal tubular piece of the connecting parts projects into the end region of the corrugated hose adjacent to the collar, and has an outside diameter that corresponds to the inside hose diameter, so the corrugated hose has a radial support at the ends and in the radially-inward direction, and the welded connection between the corrugated hose and the connecting part is facilitated. An inexpensive connecting part for the collar can be formed from the metal tubular piece through its radial expansion so that the metal tubular piece and the collar thus form a one-piece component.